docs: def geo_planar(self, surface):
          """
          Utility to convert a PlanarSurface node with subnodes
          topLeft, topRight, bottomLeft, bottomRight into a
          :class:`openquake.hazardlib.geo.PlanarSurface` instance.
  
          :param surface: PlanarSurface node
          """
          with context(self.fname, surface):
              tl = surface.topLeft
              top_left = geo.Point(tl['lon'], tl['lat'], tl['depth'])
              tr = surface.topRight
              top_right = geo.Point(tr['lon'], tr['lat'], tr['depth'])
              bl = surface.bottomLeft
              bottom_left = geo.Point(bl['lon'], bl['lat'], bl['depth'])
              br = surface.bottomRight
              bottom_right = geo.Point(br['lon'], br['lat'], br['depth'])
          return geo.PlanarSurface.from_corner_points(
              top_left, top_right, bottom_right, bottom_left)